Cold cathode gas discharge tube



March 1956 c. H. TOSSWILL COLD CATHODE GAS DISCHARGE TUBE Filed April 11, 1952 H h M r 5 A 17- Rh 1 5 E 6 WW I 1 n MHW m 11.5 B v, .5 m5

2,740,066 COLD CATHODE GAS DISCHARGE TUBE Christopher Haly Tosswill, Carshalton, England, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 11, 1952, Serial No. 281,789 Claims priority, application Great Britain April 13, 1951 7 Claims. (Cl. 313189) This invention relates to cold cathode gas discharge tubes in which the passage of current between a main cathode and the anode is controlled by the application of potentials to one or more auxiliary electrodes. Such tubes are known, having an anode, a cathode and a control-grid, which control electrode is not necessarily a grid in the mechanical sense, in which ionisation in the grid-cathode space leads to ionisation in the anode-cathode space. However, the developments in circuits in which such tubes are used, for example, computing and switching applications, demand improved characteristics, particularly, in the constancy of characteristics during the life of a tube and uniformity of operating characteristics between one tube and another of the same type.

The object of the present invention is to provide a cold cathode gas discharge tube having improved characteristics in the sense referred to above.

According to the present invention, a cold cathode gas discharge tube has an anode, a main cathode, an apertured screen and a plurality of auxiliary eletcrodes comprising at least a prirner cathode, a control electrode, which will herein be referred to as the grid, and a transfer cathode extending through the aperture of said screen, whereby a discharge can be maintained between the primer cathode and the control electrode in a space screened by the said screen from any part of the main cathode-anode path and can be extended, by increasing the potential between the grid and the transfer cathode, through the aperture in the screen into the region of the main cathode-anode discharge path, whereby the main discharge is initiated.

It is convenient to use a construction in which the main cathode is so shaped as to form the said screen.

In one form of the invention, in which this construction is employed, the main cathode is cylindrical and is arranged with its axis extending towards the anode and is closed at the end facing the anode by an apertured circular plate.

According to an alternative form of the invention, the cathode, which also constitutes the screen as in the form last described, is formed with three plane surfaces comprising a front surface facing the anode and provided with an aperture and two side surfaces extending backwards to enclose the region of the discharge between the primer cathode and the grid. In this construction, the cathode may be made of thin sheet metal or it may be of line gauze.

Such a gas discharge tube has the advantages over known types of a lower and more uniform grid striking potential because of grid-striking potential becomes substantially the same as the grid-maintaining potential and, as is known, the discharge maintaining potential of a discharge between any two electrodes in a lowpressure gas is more constant during the life of a tube and more uniform from one tube to another of the same type than is the breakdown potential between the two electrodes.

The lowering of the grid-striking potential further States Patent provides an increase in the ratio of the output potential difference of the tube, that is, the difference between anode hold-01f and anodemaintaining potentials, to the grid-striking potential. v

' In addition, the ionisation time of the tube is reduced, relatively to 'that of-tubes of known type, since the striking process of 'the tube involves the expansion of a glow-discharge already established, which is inherently faster than the establishment of a new discharge.

In order that the invention may be readily carried into effect, two examples of gas discharge tubes according to the inventionwill now be described in detail with reference to the accompanying drawings of which:

Figure 1 is a diagrammatic sectional drawing of a simple form of the gas discharge tube having a main cathode of cylindrical form which also serves as the screen;

Figure 2 isa transverse section through a gas discharge tube in which the cathode servesas the screen and comprises three plane surfaces and Figure 3 is a perspective view of the auxiliary electrodes of the tube shown in Figure 2, looking towards the rear of themain cathode. g i

The. tube shown in Figure 1 has a rod shaped anode 1 and a cylindricalmain cathode 2 of 1.5 cm. diameter and 1,5 cm. length mounted in a gas-filled envelope 3.

The main cathode 2 is arranged with its axis directed towards the anode 1, from which it is separated by about l.8 cm., and is closed at the end facing the anode by a circular plate 4 having an aperture 5 of 2 mm. diameter on the axis of the'electrode. A transfer cathode 6 is arranged on the axis of the cathode 2 and passes through the aperture 5 extending from the outside, which is the region of the main discharge, to the inside, which is the region of the auxiliary discharge. Outside the main cathode 2, the transfer cathode 6 isbent at right angles to the cathode axis and passes through a seal in the glass enevlope 3 of the tube. Arranged also on the axis of the cathode, spaced from the inner end to the transfer cathode 6 by 2 mm. and spaced from the main cathode aperture 5 by 7 Il'lll'L, is a primer cathode 7. A controlgrid 8 is mounted at right angles to the axis of the cathode with its end spaced from the ends of the transfer cathode 6 and the primer cathode '7 by 2 mm. and approximately mid-way in the gap between them. All the electrodes are of molybdenum and the gas filling is neon 99%, argon 1%, at a pressure of 20 mm. Hg. The main cathode 2 is supported by a stiff wire 9 which extends through the envelope 3 of the tube and provides an electrical connection to the cathode.

During the manufacture of the tube, a known sputtering process is used, whereby a heavy discharge is passed between the various electrodes in turn, so that someof the surface of the electrodes is vapourised and is deposited on the glass envelope. This serves to clean the surface of the electrodes and to clean up the gas, in the manner of a getter. The deposited film on the glass envelope also serves to retain any impurities in the interstices of the glass envelope.

The anode of the tube is connected through a resistance to a positive sourceof potential and main cathode and transfer cathode are connected together and to earth. The primer cathode is connected through a resistance to a negative source of potential of about 100 volts and the control-grid is connected through a resistance to a source of grid control potential.

In operation, the tube is primed by raising the grid po-' tential to about 50 volts positive with respect to the cathode, whereupon ionisation occurs between the grid and the primer. cathode and an auxiliary discharge passes between these two electrodes. This auxiliary discharge is limited to a few mici'oamperes current by the resistance connecting the primer cathode to the source of negative potential; This auxiliary discharge has no influence on conditions in the main discharge space between the anode and cathode owing to the intervening screen constituted by the main cathode. However, it has a controlling elfect on the conditions in the space surrounded by the main cathode where, in particular, the value of the breakdown potential between the control-grid and the transfer cathode is lowered, by the proximity of the auxiliary discharge, to the discharge maintaining potential between these two electrodes. Accordingly, if the grid potential is raised from the said priming value of about 50 volts to a value of about 90 volts, which is the discharge maintaining potential between the grid and the transfer cathode, the discharge which has so far existed solely between the grid and the primercathode, will extend along the length of the transfer cathode and will thus extend through the aperture in the main cathode into theregion of the main discharge path. When the leading edge of the discharge, travelling along the transfer cathode, passes through the aperture in the maincathode, the discharge will become subject to the anode-to-cathode field and ionisation will occur between the anode and the transfer cathode, leading immediately to ionisation between the anode and the main cathode.

It will be understood that the sequence of events described for the operation of the tube according to the invention is made possible by the existence of a screen, in this case the main cathode itself, separating the region of the main discharge and the region of the auxiliary discharge and the arrangement of a transfer electrode extending from the auxiliary discharge region into the main discharge region. Without the separation of these two regions, the auxiliary discharge which lowers the breakdown potential between the grid and transfer cathode would also reduce the breakdown potential between the anode and transfer cathode andthus initiate the main discharge.

it will be further understood that the operation of the tube as described does not depend on the separation of the main cathode and the transfer cathode since, in the circuit described, these two electrodes are connected together. However, when a number of such tubes are to be used in combination, there will be circuit arrangements in which the application of different potentials to these two electrodes will be of practical advantage. The triggering of the tube described depends on establishing a certain potential difference between the grid and the transfer cathode, irrespectively of the potential between the grid and the main cathode and it is therefore possible to trigger the tube by applying a negative pulse to the transfer cathode while the potentials of the grid and the main cathode remain constant.

Moreover, the primer cathode can be used as a gating electrode, since until the appropriate negative potential is applied to the primer cathode, the tube cannot be triggered by the normal operating potential difiereuce between the grid and the transfer cathode. This feature indicates an application for tubes according to the invention in electronic computing and switching circuits.

The alternative form of tube shown in Figures 2 and 3, in which corresponding electrodes are indicated by the same reference numerals as are used in Figure 1, has a moulded glass base 10 through which pass eight lead-in wires. Five of thelead-in wires are shown by the reference numerals 1l15 and appear in the sectional view of Figure 2. These lead-in Wires serve externally as contact pins for the tube and internally as supports for the electrode structure. The base 10 has a cylindrical envelope 3 butt-welded thereto. The lead-in wire 11 has a rod shaped anode ii Welded to it and this anode extends parallel to the axis of the envelope 3 for about half its length and then turns at right angles so that it faces the centre of a circular aperture 5 in the front face of the main cathode 2. The main cathode 2 is supported by stiif wires 9 which are supported from lead-in wires and, as shown in Figure 2, one of these support wires is so connected to the lead-in wire 14. The main cathode 2 also serves as the screen of the tube and has two sides extending backwards from the anode 1 enclosing the region of the auxiliary electrodes now to be described. These electrodes comprise a primer cathode 7 which is supportedfrom the lead-in wire 15 and rises parallel to the axis of the envelope to the level of the anode 1 where it turns at right angles and the end thereof is formed into a loop 16 which is opposite the aperture 5. The lead-in wire 13 supports a transfer cathode 5 which lies approximately on the axis of the envelope 3 and rises to the height of the aperture 5 where it turns at right angles and extends through both the aperture 5 and'the loop 16 in the primer cathode 7. A control grid is arranged behind the cathode 2, is supported from one of the lead-in wires not shown in Figure 2 and extends, as shown particularly in Figure 3, to near the loop 16 o the primer cathode 7.

In this embodiment, the cathode 2 is 10 mm. w1de,each '1 side extends backwards 10 mm. and the whole electrode is 50 mm. high. The front face has a circular aperture 5 of 2.0 mm. diameter 20 mm. from the top edge, 30 mm. from the bottom edge and on the centre line of this face. The primer cathode 7 is of 0.5 mm. diameter molybdenum rod and rises from the base approximately 10 mm. from the rear face ofthe cathode, extends approximately 5 mm. towards this face and is formed into a loop 16 of 2.0 mm. diameter measured from the centre of the wire, that is, the annulus formed is 1.5 mm. internal diameter. The transfer cathode 6 is of molybdenum rod of 0.5 mm. diameter. The clearance between the transfer cathode 6 and the front face of the cathode 2 is small but is not critical. The grid 8 is of molybdenum rod of 0.5 mm. diameter and rises 5 mm. from the front face and sides of the cathode. The gap between the end of the grid 6 and the periphery of the loop 16 is 2.0 mm. The main anode 1 is also of 0.5 mm. diameter molybdenum rod and the distance from the face of the cathode 2 to the top of the anode 1 is approximately 18 mm. The envelope 3 is filled with a gas filling 99% neon, 1% argon at a pressure of 20 mm. Hg.

The cathode '2 may be of thin sheet molybdenum or it may be of fine molybdenum wire gauze.

The circuit connection to the form of tube shown in Figures 2 and 3 are the same as those described for the form shown in Figure l and the mode of operation is the same.

What I claim is:

l. A cold cathode gas discharge tube comprising an envelope, a main cathode disposed within said envelope and having wall portions defining a main discharge region on one side thereof and an auxiliary discharge region on the other side thereof, one'of said wall portions of said cathode having an aperture through which the two discharge regions communicate, a primer cathode and'control electrode disposed within said auxiliary discharge region and being spaced apart a distance at which an auxiliary discharge may be effected therebetween, an anode disposed within said main discharge region and adapted to cooperate with said main cathode to produce a main discharge therebetween, and a transfer cathode extending through the aperture in the wall portion of said cathode to the vicinity of said primer cathode and control electrode and thereby existing in both discharge regions to transfer the auxiliary discharge to the main discharge region and thereby ignite the main discharge between the anode and main cathode.

2. A cold cathode gas discharge tube comprising an envelope, a cylindrical main cathode disposed within said envelope and defining a main discharge region external to said cathode and enclosing an auxiliary discharge region, a circular end wall of said cathode having an aperture through which the two discharge regions communicate, a primer cathode and control electrode disposed within said auxiliary discharge region and being spaced apart a distance at which an auxiliary discharge maybe efiected therebetween, an anode disposed within said main discharge region and facing said circular end wall and adapted to cooperate with said main cathode to produce a main discharge therebetween, and a transfer cathode extending through the aperture in the end wall of said cathode to the vicinity of the primer cathode and control electrode and thereby existing in both discharge regions to transfer the auxiliary discharge to the main discharge region and thereby ignite the main discharge between the anode and main cathode.

3. A cold cathode gas discharge tube as claimed in claim 2 in which the main cathode is constituted by gauze.

4. A cold cathode gas discharge tube comprising an envelope, a main cathode disposed within said envelope and constituted by at least three connected plane surfaces mounted to define a main discharge region external thereto and to enclose an auxiliary discharge region, the plane surface intermediate the other two surfaces having an aperture through which the two discharge regions communicate, a primer cathode and control electrode disposed within said auxiliary discharge region and being spaced apart a distance at which an auxiliary discharge may be effected therebetween, an anode disposed within said main discharge region and facing said intermediate surface and adapted to cooperate with said main cathode to produce a main discharge therebetween, and a transfer cathode extending through the aperture in said surface of said cathode to the vicinity of said primer cathode and control electrode and thereby existing in both discharge regions to transfer the auxiliary discharge to the main discharge region and thereby ignite the main discharge between the anode and main cathode.

5. A cold cathode gas discharge tube comprising an envelope, a main cathode disposed within said envelope and constituted by at least three connected plane surfaces mounted to define a main discharge region external thereto and to enclose an auxiliary discharge region, the plane surface intermediate the other two surfaces having an aperture through which the two discharge regions communicate, a primer cathode having a looped end and a control electrode disposed in the vicinity of said looped end both disposed within said auxiliary discharge region to produce an auxiliary discharge therebetween, an anode disposed within said main discharge region and facing said intermediate surface to produce a main discharge therebetween, and a transfer cathode extending through the aperture in said surface of said cathode and through the looped end of said primer cathode and thereby existing in both discharge regions to transfer the auxiliary discharge to the main discharge region and thereby ignite the main discharge.

6. A cold cathode gas discharge tube comprising an envelope, a main cathode disposed within said envelope and constituted by at least three right-angle-connected plane surfaces mounted to define a main discharge region external thereto and to enclose an auxiliary discharge region, the plane surface intermediate the other two surfaces having an aperture through which the two discharge regions communicate, a primer cathode and control electrode disposed within said auxiliary discharge region and having ends adjacent each other to produce an auxiliary discharge therebetween, an anode disposed within said main discharge region and facing said intermediate surface to produce a main discharge therebetween, and a transfer cathode extending through the aperture in the wall portion of said cathode to the vicinity of the ends of the primer cathode and control electrodes and thereby existing in both discharge regions to transfer the auxiliary discharge to the main discharge region and thereby ignite the main discharge between the anode and main cathode.

7. A cold cathode gas discharge tube as claimed in claim 5 in which the main cathode is constituted by gauze.

References Cited in the file of this patent UNITED STATES PATENTS 1,973,075 Hund Sept. 11, 1934 2,071,057 Baruch Feb. 16, 1937 2,195,505 Thompson Apr. 2, 1940 2,373,175 Depp Apr. 10, 1945 

